The fossil fuel industry for years has been purposefully misleading the American public about the scientific consensus on man-made global warming. That is the finding of a new study published in the Proceedings of the National Academy of Science that analyzed 20 years’ worth of data. The study, titled “Corporate funding and ideological polarization about climate change,” found that ExxonMobil and the Koch family foundations used similarly deceptive tactics as Big Tobacco to create doubt and confusion about anthropogenic climate change. The disinformation campaigns successfully polarized environmental issues, leading to public uncertainty and stalled policy decisions to address climate change.

“The contrarian efforts have been so effective for the fact that they have made it difficult for ordinary Americans to even know who to trust,” the report’s author, Yale University sociologist Justin Farrell, told The Washington Post. “This counter-movement produced messages aimed, at the very least, at creating ideological polarization through politicized tactics, and at the very most, at overtly refuting current scientific consensus with scientific findings of their own.”

This concerted effort over the years to create skepticism about the human causes of climate change has taken its toll. A new poll released ahead of the Paris climate conference shows that only half of the people surveyed in 20 countries consider climate change a “very serious” issue and another recent poll found that climate change is not a big concern for most Americans.

According to the international environmental organization 350.org, people should be very concerned about climate change. In an article published in Rolling Stone headlined “Global Warming’s Terrifying New Math,” 350.org founder Bill McKibben wrote about the scientific warning that we must limit global warming to 2 degrees Celsius or 3.6 degrees Fahrenheit above pre-industrial levels if we want to avoid catastrophic climate change. To meet this goal, scientists say that we can burn only 565 gigatons more carbon dioxide. But the fossil fuel industry has 2,765 gigatons of carbon in their reserves — nearly five times the safe amount.